A continuing investigation is planned of the sources and mechanisms of calcium utilization in excitation-contraction coupling in smooth muscle, vascular and nonvascular. In the guinea-pig ileal longitudinal muscle which is multiply sensitive to a variety of stimulants, Ca 2 ion uptake in response to histamine, 5-HT, sub-P and Ang. II will be determined and compared to previous data for muscarinic stimulation. Na ion uptake will be measured for these agonists. The sensitivity of Ca 2 ion uptake and Na ion uptake to receptor and Ca 2 ion channel antagonists will be determined. Biologic dose-response curves will be compared with agonist binding curves. An attempt will be made to synthesize a specific 3H-radioligand for Ca 2 ion channels and a binding assay for Ca 2 ion channels established. A comparison between receptor densities and Ca 2 ion channel densities will be made. Desensitization, specific and nonspecific, will be studied in the ileal smooth muscle as a function of Na ion, guanyl nucleotides, SH reagents and con-A. Binding measurements will be used to determine whether specific receptor changes are occuring and the effects of these perturbants on binding and on tissue desensitization compared. Long term regulation of muscarinic receptors following chronic AChE inactivation or receptor inhibition will be studied by both tissue sensitivity and ligand binding. In vascular smooth muscle from normotensive and spontaneously hypertensive rats continuation of work to define differences in Ca 2 ion utilization, and sensitivities to Ca 2 ion antagonists will be made in young prehypertensive and established hypertensive animals. A comparison will also be made after acute and chronic treatment with antihypertensive agents.